Hello! I've got a DVD9, a commercial film. And with gnome, it doesnt get mounted (nor i can mount it) if I insert it in the dvd writer. It does if I insert it in the dvd reader. I can mount it manually, using the console, though. the dvd writer is recognized as "CD-RW/DVD±RW", while the reader as "CD-ROM/DVD-ROM" maybe hal is not ready for ± (I'm just guessing)
I doubt this is the fault of sys-apps/hal. Maybe (please don't see this as offense) your DVD-writer just isn't that good in recognizing DVDs than your DVD-reader is. The quality of such drives can really vary much between the different manufactureres and even betweeen the different models of the same manufacturer. I experienced this myself with one of my DVD±RW-writers which even isn't able to read an Audio-CD without skips and cracks.
Make sure that your user is in the relevant groups (cdrom if the dvd drive is in fstab, plugdev if not). Also note that HAL will under certain circumstances not touch drives that have an entry in fstab.
Ah yes, I commented out the cdrom entry from fstab (that was only for the writer) and now it works.